I was reading an article recently in which some cartoonists were interviewed and they claimed they suffered from the same syndrome. We'd like to think that sitcom writers, or the creative types have a bank of ideas that they continually pull from, but in reality, after that initial concept has worn off, it's a day-to-day event. Ideas aren't like money that you can store and save for later. Ideas typically exist in half-conceived states until they're given time, thought, and some execution. By the time an idea is brought to life, it barely looks like its original concept.
What does this all mean? Mainly that creativity is less of a natural ability and more about hard work. If you exercise it, you'll be creative. If you don't, you won't be. Simple as that.